Field
The disclosed concept relates generally to circuit interrupters, and in particular, to circuit interrupters with temperature compensation. The disclosed concept is also related to methods of operating circuit interrupters.
Background Information
Circuit interrupters, such as for example and without limitation, circuit breakers, are typically used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition, a short circuit, or another fault condition, such as an arc fault or a ground fault. Circuit breakers typically include separable contacts. The separable contacts may be operated either manually by way of an operator handle or automatically in response to a detected fault condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open the separable contacts, and a trip mechanism, such as a trip unit, which senses a number of fault conditions to trip the breaker automatically. Upon sensing a fault condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position.
Some types of circuit breakers include a bimetal strip to provide thermal protection. Current in the protected circuit flows through the bimetal strip. Increasing current flowing through the bimetal strip causes the bimetal strip to heat up and bend. After the bimetal strip heats up enough and bends far enough, it releases a latch in the circuit breaker that causes the circuit breaker to trip. Over a period of time, low overcurrent conditions (e.g., an overcurrent that does not cause the circuit breaker to instantaneously trip) will cause the bimetal strip to heat up and cause a trip.
One problem with the bimetal strip is that it is affected by the ambient temperature. For example, when the circuit breaker is installed in an outdoor load center in a cold area, the ambient temperature in the circuit breaker will be colder than normal. The ambient temperature may keep the bimetal trip cold enough that it does not heat up sufficiently to cause a trip even when a low overcurrent condition is present.
There is room for improvement in circuit interrupters. There is also room for improvement in methods of operating circuit interrupters.